Lithium primary batteries have an average discharge voltage of about 1.5 V, and thus have compatibility with other primary batteries having an average discharge voltage of about 1.5 V (for example, manganese dry batteries, alkaline dry batteries, or the like which are hereinafter referred to as “alkaline dry batteries, etc.”). Thus, the lithium primary batteries are practically very useful. Moreover, iron disulfide (a positive electrode active material) has a theoretical capacity of about 894 mAh/g, and lithium (a negative electrode active material) has a theoretical capacity of about 3863 mAh/g. Accordingly, in the lithium primary batteries, both the theoretical capacity of the positive electrode active material and the theoretical capacity of the negative electrode active material are high, and thus the lithium primary batteries are practically very useful also as high-capacity light-weight primary batteries.
Coin-shaped (or button-shaped) lithium primary batteries and cylindrical lithium primary batteries are generally known. The coin-shaped lithium primary batteries are suitable for use in a low-load discharge region. Patent Document 1 describes that when a solvent of a nonaqueous electrolyte (hereinafter also referred to simply as “electrolyte”) contains propylene carbonate and tetrahydrofuran (THF), a reduction in closed circuit voltage at a low temperature can be limited to a lesser degree.
In the cylindrical lithium primary batteries, a positive electrode and a negative electrode are wound with a separator interposed therebetween. Thus, areas of the positive electrode and the negative electrode which face each other are larger than those in the case of alkaline dry batteries, etc. Therefore, the cylindrical lithium primary batteries are suitable for use in a high-load discharge region. Patent Document 2 describes that when a solvent of an electrolyte contains dioxolane (DIOX) and 1,2-dimethoxyethane (DME), high-load discharge performance is improved.
The intermediate-load discharge performance of lithium primary batteries is comparable to that of alkaline dry batteries, etc. To provide lithium primary batteries offering greater convenience to users, improving the intermediate-load discharge performance is required in addition to improving high-load discharge performance. It is generally said that increasing the utilization ratio of a negative electrode in intermediate-load discharge is difficult in the lithium primary batteries. The reason for this is as described below. As discharge of the lithium primary batteries progresses, elution of lithium and elution of impurities such as sulfate ions from iron disulfide occur, and the lithium and the impurities are deposited on a surface of the negative electrode. In the intermediate-load discharge, an area having a great depth of discharge is also discharged (for example, the depth of discharge is 85%). Thus, at an end stage of the intermediate-load discharge, a reaction area of the negative electrode is reduced. Moreover, a discharge current in the intermediate-load discharge is not very small, so that when the reaction area of the negative electrode is reduced, the batteries are poorly discharged.
On the other hand, it is considered that remaining oxygen in the lithium primary batteries is reduced at a surface of a carbon material (a conductive agent) in a positive electrode, thereby generating potential. Thus, it is considered that mixed potential is generated at the positive electrode of the lithium primary batteries. Therefore, although iron disulfide exhibit a potential of about 1.7 V with respect to lithium metal, the initial voltage of the lithium primary batteries (hereinafter also referred to simply as “initial voltage”) is higher than 1.7 V, and is about 1.8 V. The lithium primary batteries have such a high initial voltage, but the voltage of the lithium primary batteries (hereinafter also referred to simply as “battery voltage”) is reduced to about 1.5 V for about several seconds after application of a current load to the lithium primary batteries. Thus, it has been thought that devices drivable by alkaline dry batteries, etc. (dry battery devices) can be driven by the lithium primary batteries without problems. However, in recent years, for example, some devices including built-in semiconductor integrated circuits, as typified by digital still cameras, have been driven by alkaline dry batteries, etc. When a power source of such a device is turned on, output voltages from the batteries are applied to the semiconductor integrated circuit for several tens of milliseconds immediately after the turning on the power source. Here, if the voltage of each cell which is higher than 1.65 V (e.g., 1.8 V) is applied to the semiconductor integrated circuit of the device configured to be driven by batteries having a specified voltage of 1.65 V or lower (that is, alkaline dry batteries, etc.), the semiconductor integrated circuit may be erroneously operated. Thus, it is difficult to drive devices including semiconductor integrated circuits by lithium primary batteries, and thus devices which can use lithium primary batteries as driving power sources are limited.
Note that Patent Document 3 describes that when an electrolyte of a coin-shaped lithium primary battery contains a predetermined amount of isoxazole derivatives, an initial open circuit voltage is reduced.